1. Field of Invention
The present invention relates to the breather structure of a shaft-drive-type drive device in a shaft-drive-type power transmission mechanism for a motorcycle or the like.
2. Description of Background Art
In general, a shaft-drive-type power transmission mechanism for a motorcycle or the like is configured such that a drive bevel gear is integrally formed on a rear end of a drive shaft interlocked with an engine, and the drive bevel gear is meshed with a driven bevel gear which is pivotally supported on a rear fork and is interlocked with a rear wheel so as to transmit the rotation of the engine to the rear wheel. The drive and driven bevel gears are housed in a hermetically sealed gear chamber formed in a final casing which is mounted on one side of the rear fork. The drive and driven bevel gears are lubricated by lubricating oil sealed in the gear chamber. Further, for reducing air resistance when the drive and driven bevel gears are rotated, particularly, when the drive and driven bevel gears are rotated at a high speed, a breather mechanism for performing breathing of the gear chamber is mounted on the final casing. See, for example, JP-UM-A-58-116887 and JP-B-62-26959.
However, the conventional construction has a drawback wherein the breather mechanism for breathing is mounted on an upper portion of a gear box in a projecting manner. Thus, parts for forming the breather mechanism become necessary. Further, a portion of the breather mechanism projects from the box. Thus, there arises a drawback wherein the design property is lowered and the casing becomes large-sized as a whole.